who knows?

Date 12-23-2006 14:17

I believe it is the byproduct of burning the gas; (much like the water that comes out of the exhaust system of your car). As the part gets hotter, it evaporates more quickly, leaving the impression that the moisture actually came out of the base metal.

Charles

By Lawrence (*****)

Date 12-23-2006 14:55

Ding ding ding

First man up gets the prize!

By chuck meadows (***)

Date 12-23-2006 15:36 Edited 12-23-2006 15:50

What is the chemistry of water? H2/0. When the hydrogen is the metal meets the oxygen in the atmosphere, water (condensation) is formed, and all metal contains hydrogen. The heat from the torch allows toe hydrogen to rise to the top of the metal and unite with oxygen. At least that sounds logical to me. Is that anywhere near close to the answer?

By chall

Date 12-23-2006 16:15

I think you are headed in the wrong direction Chuck. I do not believe the simple task of preheating metal is sufficient to release the H that is part of the material chemistry.

Although I don't really like Wikipedia, this is a quick decsription of what happens:

http://en.wikipedia.org/wiki/Combustion

Scroll about half way down and you will see that the fuel burned in air yields heat, water, CO2 and N.

Charles.

By chuck meadows (***)

Date 12-23-2006 16:20 Edited 12-23-2006 16:24

Well, it sounded good when I wrote it...LOL...I guess I need to stick with topics that I know just a little bit about...Not many, but a few..

By darren

Date 12-24-2006 00:08 Edited 12-24-2006 00:15

it is amazing how angry some guys have become when i tell them the source and all sorts of arguments like its in the surface its in the air all sorts of crazy things and boy oh boy do some of them stick to their wrong answer to the point of being mad. the reason i brought this question up is to show that there are some if not alot of practices or beliefs in our trade as well as all aspects of life that are considered fact by acceptance rather than proof of fact. this forum is an indispensible asset to our trade to disseminate the proven facts and dispell the falshoods. as always i count on the incredible knowledge base that this site and my brothers and sisters of the trade possess.
as welders we are literally building the world.

another one is, if you take five pounds of pure iron and put it in water and let it turn to rust powder(FeO4) and then dry out the rust so there is zero moistureleft in the pile of rust, what does the pile of rust weigh in comparison to the 5 pounds of pure iron?
more
less
same
p.s. there is a hint in the question

to you chemists out there please give the exact amount as i am to lazy to do the math

to chall we need more guys like you in the trade

and chuck at least you had the guts to risk it and that counts for alot, good on yah, we also need more guys like you in the trade

By leon phelps (**)

Date 12-24-2006 00:36

It has been a long time since college chemistry. What I learned to do in college chemistry is to sit behind the guy with the most slanted eyes and copy dot for dot off of his test.

I think the rust would weigh more. This should be from the iron bonding to the water and stealing electrons and h20 molecules.

4Fe + 3O2 = 2Fe2O3 should be your equation.

By darren

Date 12-24-2006 03:26

some of you scholars can correct my ignorance here i would have to look it all up again as to the atomic numbers and all that other stuff but i think its something like

Fe + 1 O is black slag (that is mill scale or slag from oxy fuel cutting or the scale created from heating carbon steel orange or hotter)
Fe + 2 O is rust scale (my old chev truck)
Fe + 3 O is rust powder ( the stuff that turns water rust coloured when you disturb the cutting table)

and yes it would weigh more because of the oxygen bonding to the iron
we need a metalurgists input here and there must be a few of them in here
any help is appreciated
thanks
darren

By billvanderhoof (****)

Date 12-24-2006 06:20

It's been a long time since I took chemistry also. As Mr Phelps indicates corrosion of iron in water will result in Fe2O3. There will be a substantial amount of water trapped in the crystal structure and loosly bound to the molecules. Heating will drive most of this water out but if I remember correctly (some doubt on that) the temperature necessary to drive out the last of the water may be sufficient to reduce some of the Fe2O3 to Fe3O4 or perhaps even FeO but we will ignore that. So assuming that it is possible to produce anhydrous (no water) Fe2O3; the atomic weight of iron is 55.845 (roughly 56) and the atomic weight of oxygen is 15.994 (roughly 16) and the molecular weight of Fe2O3 is 56+56+16+16+16 or 160. For every 112 units of iron there are 48 units of oxygen. If you start with 5 pounds of iron and add 5 times 48/112 of oxygen you should get 7.14 pounds of rust.
Bill

By darren

Date 12-24-2006 06:49 Edited 12-24-2006 06:52

awsome, thanks bill,
i love this place.
it just goes to show you, you don't need to know everything about the job just your part.
darren

By medicinehawk (**)

Date 12-24-2006 11:53

You guys can intellectualize anything, but the water you burn off with a torch or drink or swim in is the same water my people have paddled in for over 80 centuries.........it comes from our Earth Mother. <
A Native Perspective.
Be well,
Hawk

By Sourdough (****)

Date 12-29-2006 21:51

All I know is that water is not condusive to making a good weld!? Alright, I said my two cents. I'm done.

By CWI555

Date 12-24-2006 16:26 Edited 12-24-2006 16:37

(My three cents worth)
There is some h2o that does get burned off via the torch. As with anything, often the truth lies in the middle. Yes; the burning of the torch pulls the moister out atmosphere giving condensation, however, there is no such thing as a dry surface unless your in the Mojave desert and not even then depending on the day. Any torch that is hot enough to pull the water out on a inter granular basis may have negative effects on the base metal, but there is that layer of moister that is not readily apparent on the surface. The condition changes with humidity level, roughness level of the material ( polished material, vs rough ground material, the later has more surface area to gather condensate.)

The first thing you see when you apply a torch to any material is the outer ring of atmospheric condensation around the flame. However; you will never see the thin layer that was on the plate. Its a factor of volume. There just isn't much volume to the layer of water that is below the visible range. As an example, there is a reason when you PT a given item that you have minimum dry dwell times (giving the cleaner enough time to evaporate before the application of the PT for instance). Just because you can't see it, doesn't mean it's not there. The same goes for a given plate or Ibeam etc.

Trying to dry a material with a torch most of the time is going to do more harm than good. I've seen a lot of people rose bud material just long enough to see the atmospheric condensate ring. This only adds to the non visible layer of H2O. What happens when you remove the torch? You have a volume of atmosphere that is less dense that the volume surrounding it. That volume will equalize with it's surrounding constituents rapidly.
However, the nature of the burnt gases that were used will bind with that same incoming volume. Unless your on thinner steel with little surface area, the steel will quickly equalize in temperature, and that will be followed by the subsequent condensation of a larger volume of that mix on the material surface. In this instance, if I've got this figured right, you've actually increased the risk, rather than decreased the risk and wasted some otherwise valuable gas and time.

On the other side of the coin, if you apply the heat 1x time again that you applied to the point of making the condensate ring go away, to a small area where you will be immediately welding, then the welding process alone will boil away the subsequent condensate that is not visible ahead of the weld and subsequent passes will maintain this condition.
If you have long seams to weld, your waisting time and money trying to get all the moister out of the entire seam area. only the first foot or two is important.

This is all assuming your material and atmospheric conditions are problematic.

In summary; 9 out of 10 times the torch is doing more harm than good. Typically that thin layer that is normally there does not harm the weld as a factor of volume. There are times depending on the material, process and atmospheric conditions, that the layer will be problematic.
In all cases, simply watching the atmospheric ring of condensate dissappear is worthless and not only worthless, may in fact create a problem.

Now that I've said my three cents worth, if there is someone out there that can prove this wrong, Im always open to education.

By HgTX

Date 12-27-2006 19:55

Torch may be doing more harm than good if your goal is to dry the material. Preheat isn't about drying, though, it's about temperature gradients and cooling rates.

Hg

By CWI555

Date 12-27-2006 21:15 Edited 12-27-2006 21:18

I believe thats what I said. PreHeat is another matter entirely. I did not address pre heat, however; in saying that, it is a factor when chasing ghost with rosebuds.

By makeithot (***)

Date 12-27-2006 22:29

CWI555,

Is not the nature of steel or metal to be porous in nature and for that reason alone contain a certain amont of moisture H2O and when heated it is brought to the surface as the molocules expand. Also depending on the gas used propane as an example which in it self is quite wet make it look like there is alot of water on the plate untill it reaches sufficent temp?

By CWI555

Date 12-27-2006 23:40

If you've got a signifigant amount of H2O in the intergranular structure of a given metal, wheither to use a torch or not will be the least of your problems.

By CWI555

Date 12-27-2006 23:49

Consider this Makeithot;

On a cool morning, do you think that moister coming out of your exaust is leaking out of the tail pipe material or is it a factor of condensation from the gases being burned in your engine? As a suggestion, try looking up some 200x pics of various grain structures, or looking up the specifics on nitriding, or underbead cracking, or hydrogen embrittlement. You may find it enlightening.
Let me know what you come up with.

By pipewelder_1999 (****)

Date 12-26-2006 02:29

I have always gone with the unconsumed hydrogen and oxygen in the flame condensing on the steel. With 9th grade being the last science class, I may be up for a "lernin" . I started to read some of the other posts and got lost on the rusted steel in water so figured I may have a stab at this.

The unburnt fuel gas can be observed when oxyfuel welding pipe so I am pretty confident it exists but would be glad to have that one explained to me too.

By darren

Date 12-26-2006 04:03

bill, lawrence maybe you could wade in here again

By Lawrence (*****)

Date 12-26-2006 04:45

I'm no chem guy or math head... but here is a bit of data

"For its complete combustion a volume of acetylene needs approximately twelve volumes of air, forming as products of combustion carbon dioxide and water vapour.

http://www.1911encyclopedia.org/Acetylene

By dasimonds (**)

Date 12-26-2006 22:35 Edited 12-26-2006 22:41

There was a good discussion a while back. Try a search for "Moisture From Preheating".
Dale Simonds

By billvanderhoof (****)

Date 12-27-2006 07:48

And while the temperature of the steel is below the dew point temperature of the flames combustion products the water vapor will condense on the steel.
Bill

By joseph asturino (*)

Date 01-01-2007 15:40

hay pipe welder , remember me , (questions on the CWI exam)....anyway , go to "certification",,,,,,,my question is under "AWS certs" scroll down past your responce , and 12 down is AL "one wing AL",,,,explaining where the water comes from.....

P.S. where are you from....?

By Cgregory (**)

Date 12-27-2006 15:37

Combustion produces water and CO2 as byproducts.

By CWI555

Date 12-27-2006 21:14

Yes it does, It's those by products that are the problem.

By dmilesdot (**)

Date 12-28-2006 15:56

Ever look at the other side of the steel being heated. No condenstation there. Must be the torch!

By agong

Date 12-28-2006 18:44

Hi Everyone,
Happy New Year!

The water is not coming from the torch when the steel is heated. Do this test: Preheat the same plate in the same area twice in 5 minutes, see if there's water when you do the second time.
The water comes from Water of adsorption on the plate surface + Water of crystallization in the rust.
Iron Rust=FeO+Fe2O3+Fe3O4+H2O+FeCl- +OH- ..., it's a continuous chemical reaction. The water (comes from air or rain) is very easy to get crystallized with rust and stays on the plate.
Water of adsorption:Moisture in the air is adsorbed by the plate surface.

Gong

By jon20013 (*****)

Date 12-28-2006 18:54

Good theory, but why does the same thing happen on stainless steels then? (visually rust free). I have heard many theories but find most of my mind standing on the by-product of combustion side of the discussion.

By agong

Date 12-28-2006 19:03

Water of adsorption

By hogan

Date 12-28-2006 19:34

try it with electrical heat, any water

By Lawrence (*****)

Date 12-28-2006 19:38 Edited 12-28-2006 19:48

Agong

The water does not appear on the second heating simply because the metal is already heated beyond the dew point.

Water *is* a by-product of the oxy-fuel process... This is a fact and not really up for debate. When and how and why that by-product water attaches itself to steel plate and when it evaporates is very interesting.

What is happening is more closely related to water forming on the outside of a glass of an iced drink on a warm day.

Go ahead and remove all rust and mill scale from your steel and then cool it below the dewpoint. The water from your oxy-fuel flame will adhere until the part is warmer than the dew point.

Water can only crystalize below it's freezing point, it will not crystalize within a rust matrix unless temperature dictates it to freeze. Water will only make for wet rust. If an electric blow dryer was applied to the steel as mentioned above the heat could be the same with no water being visible on the steel.

If you hit the steel with a hammer or put it in a vice will water squeeze out?

Carbon can migrate into steel in solid solution... Water will not.

By agong

Date 12-28-2006 21:24

Lawrence,
"Water can only crystalize below it's freezing point, it will not crystalize within a rust matrix unless temperature dictates it to freeze." This is not true.
Please see: http://en.wikipedia.org/wiki/Water_of_crystallization

Water *is* a by-product of the oxy-fuel process..., I agree with this but with heating for a while the temperature of other area of the plate should be higher than the dewpoint... but water still can be seen following the movement of the torch. Does that water come from the "by product"?

I will do more test later.
Regards,
Agong

By CWI555

Date 12-29-2006 03:05 Edited 12-29-2006 22:23

I agree with the idea that you can have small quantities of water on the plate surface for various reasons, but the primary source when using a torch is the condensation formed by the combustion of the gases. It's a waste of gas to "cook the water out of the steel". There is no such thing.
Use a STM to measure the diameter of a water molecule, then use a SEM to measure the gap between grains in A36 steel and tell me where your going to fit a water molecule in. It's not going to happen.

By darren

Date 12-28-2006 22:27

wow

By 803056

Date 12-29-2006 02:52

This was my in reply, with a couple of grammar corrections, to a similar question that was asked in a different thread.

Hello Joe;

I read the other post where they were discussing "where does the water come from?" Interesting, very interesting.

The water is a byproduct of combustion. Whenever you burn a hydrocarbon, you produce water (H2O) and carbon dioxide (CO2). I don't care if you burn wood, natural gas, or acetylene; the end products include H2O and CO2. Sorry I can't make the numbers subscripts.

We did an experiment in Physics class once where we had to calculate the BTU (heat) content of natural gas. We placed a Bunsen burner in a dish and placed both under a boiler. We measured the flow of water and recorded the inlet temperature and the outlet temperature. We also measured the volume of gas being burned. Several of the students requested new boilers because their dishes were rapidly filling with water from their leaking boilers. The professor just laughed and turned to me; he called me "his little dummy welder", and said, "Tell all these smart people where the water is coming from."

They didn't believe all that water could possibly be coming from the combustion of the gas, but let me assure you, it did. 26 pounds of acetylene produces about 18 pounds of water that condenses on the cold surface during the combustion process. If you were to keep the base metal surface below the dew point, as we did with the boilers, you would not see the "wet spot" disappear. Think of the warm moisture laden air condensing on cold water pipes in the summer.

I don't know where you live, but here in New England, on cold winter mornings water runs out of the exhaust pipe of our cars and trucks until the exhaust system heats up. Every gallon of gasoline produces about a gallon of water when completely combusted.

So, now you tell me, is it a good idea to use a propane fired gas range to store low hydrogen coated electrodes on a field site? What is the burning fuel producing? Are the electrodes exposed to the gases produced by combustion? What's the difference between steam and water?

I was preheating a heavy column in the field in early February many years ago. Once the column was heated, I turned the flame down low so that I didn't overheat the column, but did maintain the preheat temperature. By the time I had the column welded, I had an icicle hanging down in the web that was about three foot long. The foreman accused me of melting the snow off the roof some five stories above my head. No one said you had to be the smartest man on the job to be the foreman.

How many times have you been told to drive the moisture out of the steel before welding? I've heard it many times. Then, once the part is heated, the welders go on coffee break or off to lunch and then resume welding without reheating the part. After all, they already drove the moisture out of the steel. Meanwhile, I get my butt chewed for wasting gas and time trying to "stay warm" as I maintained the required preheat temperature. I never told the foremen they were idiots or dumb as rocks. I just collected the overtime repairing everyone's cracked welds. The wheelbarrows were full and heavy, but the bank never once refused the money.

As for the steel absorbing moisture; think about it, how thick is a beer can? If the steel (or aluminum) was porous we would not be able to buy beer in cans. The beer would leak out. If steel was porous, you would never get me into a submarine. The water molecule is rather large. The pores in the steel would have to be large enough to accommodate them. We wouldn't need screens for our windows, we could use quarter inch thick plate! Ok, ok, I'm getting carried away, but you get the idea.

Happy New Year!

Best regards - Al

By Shane Feder (****)

Date 12-29-2006 08:36

Excellent explanation Al,
Happy New Year to you and the rest of the members on the forum,
Regards,
Shane